1. Field of the Invention
The present invention relates generally to humidifiers and, more particularly, to a system for measuring one or more operating conditions of a humidifier. Moreover, the present invention is directed to a system for detecting the output efficiency of a humidifier and the level of liquid retained within the reservoir of a humidifier.
2. Description of the Prior Art
Various types of humidifiers are utilized to provide moisture to indoor air and thereby modify the relative humidity. Included among such humidifiers are ultrasonic humidifiers, steam humidifiers or vaporizers, and evaporative humidifiers.
Evaporative humidifiers typically include a housing having a reservoir of water and a stationary evaporative media, usually a wick assembly supported within a housing. The reservoir is usually provided in fluid communication with a water tank for providing an extended supply of water. The lower portion of the wick assembly is positioned within the reservoir to absorb water contained therein. Air is blown through an upper portion of the wick assembly, thereby causing evaporation of the water from the wick assembly and subsequent transfer of the evaporated water to the ambient air.
Moreover, water within the wick undergoes a phase change as it adsorbs the heat of vaporization from the ambient air, thereby depressing the temperature of the air, wick and reservoir water. As such, a temperature differential exists between the air inlet and the air outlet of a conventional evaporative humidifier due to the evaporation of water. If a stationary wick assembly is utilized, the level of water within the reservoir should remain relatively constant to provide for both continuous adsorption of water by the wick assembly and sufficient air flow therethrough. An example of an evaporative humidifier is disclosed in U.S. patent application Ser. No. 09/637,484 filed, Aug. 11, 2000, now U.S. Pat. No. 6,427,984 which is assigned to the assignee of the present invention and is incorporated herein by reference.
In the interests of both energy conservation and safety, many humidifiers have control systems that de-energize an electrical output device in response to the water level in the reservoir falling below a certain level. For example, it is well known to provide a float assembly within the water reservoir for deactivating the humidifier when the water level within the reservoir is deficient. The typical float assembly includes a float and a rod extending upwardly from the float. The float rod has traditionally been supported by a stationary retainer either fixed to the inside of the humidifier housing or to a wick support frame. When the water level within the reservoir is adequate, the upper end of the float rod closes an activation switch and the humidifier operates. As the water level falls, the float rod descends, until the rod no longer closes the activation switch, at which point the humidifier is deactivated. An example of such a prior art float assembly is disclosed in U.S. Pat. No. 5,945,038.
Although providing a desired deactivating function, prior liquid level response control systems have typically exhibited certain deficiencies such as high cost, erratic performance, and cumbersome design. Additionally, humidifiers utilizing a conventional float assembly de-energize the humidifier and/or indicate an out of water condition, as soon as the water level is insufficient to create enough buoyancy to close the activation switch. This condition generally occurs well before all of the water has evaporated from the reservoir and wick. As such, a wet or damp wick often rests in standing water for an extended period of time.
Therefore there remains a need in the art for a humidifier including a system for accurately providing an indication of an insufficient water level in a supply reservoir.
Additionally, the prior art fails to provide a system for providing an accurate indication of the operating efficiency of the humidifier. More particularly, as water is evaporated from the wick, minerals and other pollutants contained in the water will typically remain on the surface of the wick. As the wick ages, this plating action reduces the wetted surface area of the wick. Since the amount of heat adsorbed by the water from the ambient air is dependent on the wetted surface area, the overall efficiency of the humidifier will decrease proportionately with the wetted surface area lost as the wick ages. When the output efficiency of the wick reaches a predetermined end of life condition, it is desirable to replace the wick. The prior art humidifiers fail to provide an accurate and reliable system for providing an indication of wick output efficiency and the need to replace the wick.
Therefore, there remains a further need in the art for a humidifier including a system for measuring output efficiency and for providing an indication of the need to replace the wick.
The humidifier of the present invention includes a reservoir adapted for retaining a liquid. A humidification unit, comprising a blower assembly, is provided for treating ambient air with the liquid. The blower assembly includes a housing, a motor supported by the housing, and a fan supported within the housing and operably connected to the motor. The housing includes an air inlet, an air outlet and an evaporate air flow path extending between the air inlet and the air outlet. An evaporative media is in fluid communication with the liquid within the reservoir and includes a portion extending into the air flow path of the housing.
A reservoir temperature sensor detects a temperature within the reservoir at a predetermined low liquid level and produces a reservoir temperature signal indicative thereof. An air inlet temperature sensor detects a temperature of air prior to the air passing in contact with the evaporative media and produces an air inlet temperature signal indicative thereof. An air outlet temperature sensor detects a temperature of air after the air passes in contact with the evaporative media and produces an air outlet temperature signal indicative thereof. A controller is provided in communication with the reservoir temperature sensor, the air inlet temperature sensor, and the air outlet temperature sensor for receiving the reservoir temperature signal, the air inlet temperature signal, and the air outlet temperature signal, respectively.
The reservoir temperature sensor, the air inlet temperature sensor, and the air outlet temperature sensor may be utilized in various combinations to determine any one or more of the following operational statuses of the humidifier: (i) output efficiency of the evaporative media, (ii) a low liquid condition, (iii) a dry evaporative media condition, and (iv) an aged evaporative media condition. All of these operational statuses or operating conditions may be determined by the controller initially calculating a first differential between the air inlet temperature and the air outlet temperature as indicated by the air outlet temperature signal and the air inlet temperature signal. To arrive at a value for the output efficiency, the controller compares the first differential to a predetermined differential of a new, or fully efficient, evaporative media. The efficiency of the new wick is a function of the structural features and material properties of the humidifier, including the wick, along with operating and environmental conditions. A display provides the user with an indication of the determined output efficiency.
The controller may distinguish between the low liquid condition, the dry evaporative media condition, and the aged evaporative media condition by analyzing the first differential and the reservoir temperature signal. In one embodiment, the controller determines whether the low liquid condition exists by calculating a second differential between the air inlet temperature and the reservoir temperature. When the magnitude of the first differential is not greater than a first predetermined amount and the magnitude of the second differential is not greater than a second predetermined amount, then the air inlet temperature is substantially equal to the reservoir temperature, indicating that the liquid in the reservoir has fallen below the low liquid level. In response, the controller generates a low liquid signal for activating a refill indicator. When the magnitude of the first differential is not greater than a first predetermined amount and the magnitude of the second differential is greater than as a second predetermined amount, then the air inlet temperature is not substantially equal to the reservoir temperature, indicating that the liquid in the reservoir has not fallen below the low liquid level. In response, the controller generates an evaporative media condition signal for activating a replacement indicator.
The first and second predetermined amounts are empirically determined and are dependent upon the structure of the humidifier, including the size and material of the reservoir, and environmental and operating conditions, such as the temperature of ambient air, the relative humidity of ambient air, air flow velocity, evaporative conditions of the wick, and the temperature of the liquid as supplied to the reservoir.
In another embodiment of the humidifier of the present invention, a differential between the air inlet temperature and the reservoir temperature is determined by the controller and compared to a predetermined value. The controller detects the low liquid condition and generates a low liquid signal when the magnitude of the differential is not greater than the predetermined value, thereby indicating that the air inlet temperature is approximately equal to the reservoir temperature. Again, the predetermined value is empirically determined and is based upon the structure of the humidifier, as well as environmental and operating conditions.
In a further embodiment, the controller determines the low liquid condition by comparing a differential between the air outlet temperature and the reservoir temperature to a predetermined value, which again is empirically determined and dependent upon the structure of the humidifier, environmental conditions, and operating conditions. The controller generates a low liquid signal when the magnitude of the differential is greater than the predetermined value, thereby indicating that the air outlet temperature differs substantially from the reservoir temperature.
In yet another embodiment of the humidifier of the present invention, the controller generates a low liquid signal when the reservoir temperature increases by at least a predetermined amount within a predetermined number of periods of elapsed time. In still another embodiment, the controller generates either an evaporative media condition signal or a low liquid signal when the air outlet temperature increases by at least a predetermined amount within a predetermined number of periods of elapsed time. The predetermined amounts of temperature and time are empirically determined and, again, are based upon the structure of the humidifier, as well as environmental and operating conditions.